Traditionally parts, which form the body of various wind instruments and guitars, are mainly made of wood. Wood is an excellent material in terms of sound engineering because wood is extremely stiff material in respect of its weight, and its vibrating properties generally please the human ear. The length of tone is suitably short while wood suitably damps the vibration.
The problem of wood is the fact that it is laborious and relatively slow to work to achieve the exact shape and degree of finishing (for example desired coarseness of the surface) required. In addition, the inconvenient influence of pores, possible resin pockets in grain structure and other invisible unevenness on the surface of wood often appear only while testing the finished instrument. In the most disadvantageous situation you may notice that the great amount of work done for manufacturing a musical instrument has been wasted and the instrument has to be rejected due to its unqualified tone.
For example, working a neck of an electric guitar is an especially laborious and skill requiring working phase, while space must be prepared for a truss rod, which functions as a counterforce against the pull of the strings inside the neck. Three alternative techniques have become common in preparing the space for a truss rod; in the first alternative the lower part of the neck is made of one object to the upper surface of which a groove is worked for a truss rod, and after mounting the truss rod, an upper part made of separate object is mounted on the lower part. In the second alternative a groove is made to the lower surface of the neck reaching above the middle point of the cross-section of the neck, which groove is plugged after mounting the truss rod by glueing a covering object of the length of the groove and of the thickness less than the depth of the groove to the groove under the neck. In the third alternative the neck is made of two halves of the neck divided horizontally in the middle, to sides, which are to be glued against each other, of which a groove has been made vertically at the same place. In all these cases, the neck parts are glued together. Glueing requires great exactness and it always worsens the tone properties of the finished neck, while the glue material remaining in the connection behaves acoustically differently than the surrounding wood.
In use, wood also encounters very annoying problems, which are due to swelling, and shrinking (so-called humidity-related dimensional changes) caused by humidity of the air. For example, the tuning state of an electric guitar may change due to the different degree of humidity and its changes at a concert region (continental climate, sea climate) even during a concert. Sometimes the humidity of the air may increase in a concert hall also, for example, due to a great number of people.
Changes due to humidity cause problems also in respect of the finishing stage, while parts experiencing no changes due to humidity must be attached to wood, for example, frets made of metal, tuning mechanisms and so on.
Especially troublesome are dimensional changes in typical enlarging direction of wood, e.g. against grains, on the neck area of an electric guitar due to humidity changes. In the neck of an electric guitar it means the same direction in which position the earlier said frets made of metal are. In case a guitar has been manufactured and finished in a damper place than the place of use is, the end of frets stick out in more dryer conditions, and may even harm the fingertips of the player.
Further, the problem with wood is, among other things, the fact that many species of wood suitable for material of musical instruments are endangered nowadays. For example, ebony and Brazilian rosewood are protected in many countries.
Problems of wood instruments have been tried to avoid by facilitating various plastic and composite manufacturing techniques. The humidity-related dimensional changes of necks have been decreased, for example, by mounting aluminium strips to the neck, manufacturing the neck of wood enforced with carbon fibre or thermoset compound enforced with carbon fibre. The humidity-related dimensional changes have also been tried to minimize with heat treatment of wood.
In addition, the body of a guitar, among other things, has been made by injection moulding of acryl (PMMA) or some other amorphous polymers, for instance. The method is excellent in terms of production, while in this way, the body part will be of extremely uniform quality and the final shape may be achieved straight without separate finishing stages.
Non-enforced plastics commonly used in injection moulding of the body of an electric guitar are acoustically not as good as wood. The duration of tone is longer, stiffness smaller and these together create a “hollow” and “monolevel” sound, which is hard to define. In addition, so called “attack”, that is the sensitivity of a tone to kindle in an electric guitar with this kind of a body remains on a modest level.
Acoustic disadvantages of a body made by injection moulding have been tried to be reduced by lowering the specific weight of material with various flotation techniques. Stiffness has been tried to increase by adding various reinforcements, such as fibreglass or carbon fibre. Results from both ways have remained acoustically modest while both said reinforcements increase the specific weight of the material and lengthens the duration of tone, that is the inner dampening having influence on the duration of tone remains on a modest level.
The object of the invention is to provide a method for manufacturing a musical instrument or its parts, with the use of which the earlier said problems related to recognized manufacturing methods of musical instruments and to musical instruments manufactured by those are eliminated. Especially, the object of the invention is to provide a method, with which musical instruments or its parts may be manufactured of plastic materials such that tone, corresponding to a high quality musical instrument made of wood is achieved. In addition, the object of the invention is to provide a musical instrument manufactured with the method in accordance with the invention.